Colyn:

I do not know the answer to that. The basic design flaw is one that TCM corrected on their crankshafts some time back and it probably continues to exist in all of the Lycoming cranks--but I do not KNOW that to be true. I haven't looked at all of the Lycoming cranks. There seem to be two issues. ONE, is the filet radius and TWO is the design strength margin. Both appear to be marginal in the Lycoming IO-540 cranks.

The weird thing about crankshafts is that they can react to various inputs in what seem to me to be unpredictable ways. For example, we see cranks that appear to be very strong at certain rpms and then marginal or unacceptable at other rpms all as a result of the torsional loads that are realized. As far as I know, there is no way to predict that. It has to be measured. Some of these changes in stress are quite surprising. I'd like to know more about them. Two of the factors that seem to be of significance are rpm and peak pressure. Notice MEAN PRESSURE (or HP) is not the biggest factor, it's other, more difficult to quantify factors that have to be measured on the running engine. I have seen engines run with lower crank torsional stress at higher powers with those factors controlled and have very high torsional stress at lower powers with the wrong thetaPP and rpm combination. Tis a puzzlement.

Crankshafts lead a difficult life and I've grown to appreciate that we can put them through mighty tough times by accident.

Walter


On Jun 27, 2005, at 5:18 PM, colyncase on earthlink wrote:

3)  There has been compelling evidence shown that the Lycoming crankshaft
> problem is one of design, not manufacture.
> 
>  Walter
 
Walter,
 
Do you happen to know if the 580 uses the same crankshaft and/or if it has
more or less strength margin at stock power than the 540 crankshaft?
 
Colyn